Studies with highly purified preparations of cells from collagenase digests of gastric mucosa suggest that in some species histamine (and histidine decarbosylase) is located in mast cells which lay in close proximity to the parietal cells. In rodents, these substances are present in enterochromaffin-like (ECL) cells which are embedded in the pit of the gastric gland. The major histamine metabolizing enzyme activity in dog gastric musoca is histamine methyltransferase which is located in the parietal cell and in rat, diamine oxidase (location undetermined). Conditions for a short term culture of the histamine containing cell have been established but, so far, histamine release has not been observed with a variety of gastric hormones and neurotransmitters. Studies in patients with duodenal ulcers have shown that following an infusion of histamine, the amine is cleared less rapidly from the circulaton than in normal subjects.